As solid-state imaging devices, there is an amplification type solid-state imaging device represented by a MOS type image sensor such as a complementary metal oxide semiconductor (CMOS). In addition, there is a charge transfer type solid-state imaging device represented by a charge coupled device (CCD) image sensor.
These solid-state imaging devices are frequently used in digital still cameras, digital video cameras, and the like. In recent years, as solid-state imaging devices have been mounted in mobile apparatuses, such as mobile phones and personal digital assistants (PDAs) with cameras, a MOS type image sensor has been frequently used from the viewpoint of having a low power supply voltage, low power consumption, and the like.
The MOS type solid-state imaging device includes a pixel array (pixel region) in which a plurality of unit pixels are arranged in a two-dimensional array form and a peripheral circuit region, and each of the unit pixels includes a photo diode which is a photoelectric conversion portion and a plurality of pixel transistors. A plurality of pixel transistors are formed of MOS transistors, and generally comprise three transistors including a transfer transistor, a reset transistor, an amplification transistor, or four transistors additionally including a selection transistor.
In addition, in the above-described solid-state imaging device, a stacked structure has been proposed in which a plurality of semiconductor substrates having different functions are stacked in an overlapping manner and are electrically connected to each other.
In the stacked structure, since each circuit can be formed optimally so as to correspond to the function of each semiconductor substrate, it is possible to easily realize high performance of a device.
For example, it is possible to manufacture a high performance solid-state imaging device by optimally forming a sensor circuit and a logical circuit so as to correspond to respective functions of a semiconductor substrate including the sensor circuit and a semiconductor substrate including the logical circuit in which a circuit processing signal is provided. At this time, through electrodes are provided in substrates of the semiconductor substrates, and thereby the plurality of semiconductor substrates are electrically connected to each other.
However, if a semiconductor device is formed by connecting different substrates to each other by using a connection conductor which penetrates through a substrate, it is necessary to form a connection hole while maintaining insulation in the deep substrate, and thus a practical use is difficult from the viewpoint of economic costs of a manufacturing process which is necessary in creating the connection hole and embedding the connection conductor.
On the other hand, for example, if a small contact hole of about 1 micrometer is to be formed, it is necessary to thin an upper substrate to the utmost limit. In this case, complex steps such as, attaching the upper substrate to a support substrate before being thinned and an increase in costs may result. In addition, in order to embed a connection conductor in a connection hole with a high aspect ratio, a CVD film having a good coatability property, such as tungsten (W), is necessarily used as a connection conductor, and thus materials to be used as a connection conductor may be limited.
Therefore, a manufacturing method of a semiconductor device such as a solid-state imaging device has been proposed which achieves a high performance by sufficiently exhibiting each performance, mass productivity, and a reduction in costs (for example, refer to PTL 1).
PTL 1 has proposed a stacked structure in which a support substrate of a rear surface type image sensor is stacked as a logical circuit, and a plurality of connection contacts are provided from the top by using a thinning step of the image sensor.